This invention relates generally to turbomachinery and, more particularly, to a segemented damper for a turbomachine blade.
The invention described herein was made in the course of or under a contract, or a subcontract thereunder, with the United States Department of the Air Force.
In turbomachinery rotor assemblies of the type having a plurality of blades extending radially from a rotor, wheel or disk, a common problem encountered is the vibration which occurs between the rotor disk and the blade or between the blades themselves. The occurrence and degree of this vibration is a function of many factors, as for example gas temperature, turbine speed, and the method by which the blades are retained within the rotor. Generally, any vibratory displacement which occurs is most severe in the blade tip but the effects thereof may act on any portion of the blade to eventually cause undesirable fatigue failure. Other undesirable effects of the vibration include the complications of suitably retaining the blades within the disk. One common method by which the effects of the vibratory forces are lessened is that of using blade shrouds to interconnect adjacent blades so as to provide a mutual damping function to the combination. In some blade combinations a blade tip shroud has been found suitable for the purpose, while in other applications a midspan shroud has been found to more accurately prevent blade vibrations. Other methods of attaining this function include various schemes by which the damping function is applied to the root of the blade or at some place in the blade retaining device. However, a common problem exists in the various prior art methods in that they generally offer mechanical complications of installation, or involve expenses which cause them to be prohibitive.
A common approach is to employ a ring which is attached at its inner portion to the disk by bolts or the like, and which extends radially outward to act at its intermediate point as a blade retainer device and at its radially outer point as a blade damper device. Such a design relies on the mechanical interference of the ring and the disk to provide the required damping of the blade and is further inherently dependent on the ring-to-blade interference. Where high temperatures are involved, as in a turbine, the retainer ring must be temperature/creep resistant in order to ensure good damping engagement with the blade. Further, such retainers are generally manufactured of forged materials which are less capable of withstanding high temperature exposure. Another complication is that thermal hoop stresses are caused in such a ring arrangement, especially during turbomachine acceleration and deceleration. Such high stress temperatures, therefore, tend to limit the low cycle fatigue life of such a ring retainer.
It is therefore an object of the present invention to provide a blade damper which is not dependent on temperature and creep strength for proper performance.
Another object of the present invention is the provision for a blade damper which is not subject to hoop stresses caused by high temperatures.
Yet another object of the present invention is the provision for a blade damper which is not composed of a forged material which is incapable of withstanding high temperature exposure.
Yet another object of the present invention is the provision of a blade damper which is not susceptible to low cycle fatigue caused by cyclic variable operation.
A further object of the present invention is the provision of a blade damper which is relatively easy to manufacture, simple to assemble, and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.